Coating guns are typically mounted on programmable industrial robots for use in automated production lines. The robots are advantageous for applying an even coating of powder to irregular shaped articles. The robots can be programmed to coat articles with different configurations and to coat successive articles different from previously coated articles. For example, U.S. Pat. No. 4,798,341, discloses an improved coating gun for mounting on a programmable industrial robot. This patent is directed to the application of a liquid spray by a single coating gun.
Normally, a wrist component is attached to the end of the robot arm for mounting the coating gun. The arm moves to position the coating gun in space and the wrist component provides two or three axes of motion for aiming the coating gun relative to the end of the robot arm. However, there is a limit to the weight which can be mounted to the end of the robot arm without interfering with the operation of the robot. Also, the robot mounted guns are typically not easily removed from the robot and sometimes require excessive system downtime for repairs.
In certain powder coating applications, it is desirable to provide two coating guns within a single housing so that the desired spray pattern is formed with a desired direction and/or shape. While the provision of twin guns in a single housing is known, the guns have typically been secured within the housing in a single position. When an operator desires to change the direction or adjust the shape of the spray pattern, the housing is typically removed from the robot arm and replaced with a different housing wherein the two guns are repositioned to direct the spray in a different direction or to form a desired spray pattern shape. This procedure can be expensive because it requires stocking a number of different coating guns housings, each locating the guns in a different position. Alternatively, one set of coating guns can be removed from one housing and assembled in a different position in another housing. While there is a financial savings in reducing the number of guns carried in inventory, the disassembly and replacement is a time consuming operation which can still be expensive because of excessive system downtime.
Another problem in assembling or replacing guns within a housing is that the powder and electrical connections between the robot and the coating guns are typically provided by rigid tubes which are shaped to accommodate a specific mounting position. Therefore, if the position of the coating guns in the housing is changed, the connecting tubes may also have to replaced or bent to a different configuration to accommodate the repositioned powder guns. Both of these possibilities are expensive because they require a larger parts inventory and can be a time consuming activity which causes excessive system downtime.
An electrostatic powder coating gun periodically requires cleaning to remove powder which builds up within the gun, primarily within the nozzle of the gun. Cleaning the nozzle is also required whenever the powder color is changed. Cleaning the gun can be time consuming for the operator and result in excessive system downtime.